Roast the capsicum a day ahead (to save time) if you can. Preheat the oven to 200°C (180°C fan-forced) and cook it in a baking dish for about 30-40 minutes until the skin blackens.
When the capsicum is cool enough to handle, peel it, then remove the top and the seeds. Then dice the capsicum.
Place the green beans in a shallow bowl of boiling water for 2 minutes. Then drain and refresh them in cold water.
Arrange the green beans, tomatoes and capsicum on two plates, then scatter with olives and capers. Drizzle with the French vinaigrette and garnish with parsley leaves.
Season the tuna steaks with salt and pepper and brush them with olive oil.
Heat a skillet over medium-high heat.
For a rare steak, cook the tuna for about 1 1/2 to 2 minutes on each side.
Place the tuna steaks on top of the salads and add a dollop of green sauce. Serve immediately with the potato chips on the side.